This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-068766, filed Mar. 13, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a novel porphyrin metal complex and a method of preparing the same. More specifically, the present invention is concerned with a mercapto-substituted imidazolylporphyrin metal complex monomer and a polymer having the monomer as a constitutional unit, and methods of preparing the monomer and the polymer. The polymer provided by the invention is capable of being connected to an electrode via the mercapto group contained in the polymer.
The polymer having the porphyrin metal complex monomer of the present invention as a constitutional unit, may be used as energy transfer devices for transferring photonic energy and electronic energy of the order of nano-meter to sub-micrometer. More specifically, the polymer having the porphyrin metal complex of the present invention as a constitutional unit is applicable to materials for use in artificial photosynthesis systems, solar batteries, and the like.
The porphyrin metal complex is constituted by four pyrrole nuclei, four methine groups and a metal ion. Each two of the four pyrrole nuclei is cross-linked by one methine group to form cyclic tetrapyrrole, and a metal ion is inserted into the center of the cyclic tetrapyrrole. The porphyrin ring, when one of its double bonds is reduced, is referred to as xe2x80x9cchlorinxe2x80x9d. When a magnesium (II) is inserted as a central metal ion in the chlorin skeleton, the resultant structure is called chlorophyll. Chlorophyll is used in a photosynthetic protein system, where it serves as an antenna complex for trapping and transferring photonic energy and also serves as a special pair and pheophytin, into which no metal ion is inserted, responsible for electron transfer. And then, electrons are finally transferred to benzoquinonyl and stored therein.
The electric wire constructed at a molecular level is important since it may be used in photovoltaic devices or photosynthetic systems for transferring electrons and energy. From this point of view, various studies have been made. Since the porphyrin metal complex has characteristics exhibited by conjugated xcfx80 electrons, it is suitable for a material which forms a molecular-level electric wire. There have been some reports on the porphyrin connected to a gold electrode or the like.
For example, Sakata et al. have reported that a porphyrin unit is self-organized over the surface of gold via a thiol group (Chem. Lett. 1447 (1994), Chem. Lett. 907 (1996), Chem. Commun. 57 (1998), Chem. Lett. 267 (1988)). Although they perform electrochemical measurements and experiments on photoirradiation on the surface of the gold electrode, they fail to develop an electric wire of the porphyrin polymer. Lindsey et al., have recently succeeded in synthesizing a porphyrin monomer using a thiol derivative as a substituent (J. Org. Chem, 64, 8635 (1999)). The use of the thiol derivative provided an interesting finding: an acetyl derivative can be connected onto the surface of gold but a pivaloyl group cannot. However, the porphyrin polymerization through covalent bonds have not yet been attained. There are two problems in forming the porphyrin polymer by a covalent bond and using it as a wire. First, much time and effort are required for polymerization and purification of the porphyrin polymer. Second, it is difficult to reconstruct or cleave the polymer array. It has not yet been reported that the wire of the porphyrin polymer has been successfully developed. On the other hand, Takahashi et al., have studied porphyrin in an attempt to use it as a material for a solar battery (J. Phys. Chem. B, 103, 4868 (1999), J. Phys. Chem. B, 101, 991 (1997), J. Phys. Chem, 91, 3055 (1987)). They employ a simple porphyrin compound or a mixture thereof. As a result, they attained a photocurrent rate of a maximum 18.9%. However, the solar battery admits further improvement in a method of connecting the wire to an electrode and in selection of porphyrin compound to be employed in the wire.
An object of the present invention is to provide a device in a length of tens to hundreds nanometer for transferring photonic energy and electronic energy, which is expected to be applied into artificial photosynthesis and novel materials for solar batteries. More specifically, the object of the present invention is to provide a device of a self-organized type, which is capable of connecting tightly and stably to a surface of an electrode and which is easy to cleave and reconstructed.
Another object of the present invention is to provide a method of preparing the aforementioned device.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.